This invention relates generally to a three-degree-of-freedom and three-arm industrial robot of a horizontal multi-joint type, and particularly to an art of saving space for installing the robot.
Conventionally, there has been known an industrial robot wherein first, second and third arms are sequentially attached from a base, a robot hand for conveying a workpiece is linked to a distal end portion of the third arm, and arms and robot hand are rotated by rotational driving force. Although this robot is assumed to fold its joints into two different directions with respect to one movement position, the conventional robot is composed such that the joints always fold in one same direction.
However, the above-mentioned conventional control method of folding the joints has a problem that, when the robot is composed such that joints always fold in one same direction, a distal end portion of the second arm extends beyond the distal end portion of the third arm with respect to a forward direction of a workpiece in some position. In such a position, the distal end portion of the second arm is to obstruct the workpiece conveying, which increases a movable area that makes no contribution toward conveying the workpiece, so that space for installing the robot becomes larger.
This invention is made to solve the above-mentioned problems. The first object of the present invention is to provide a horizontal multi-joint industrial robot wherein a movement area that makes no contribution toward conveying a workpiece, is minimized by controlling folding directions of robot joints, thereby saving space for installing the robot, and provide a control method thereof.
In order to achieve the above-mentioned object, according to one aspect of the present invention, there is provided a horizontal multi-joint industrial robot in which at least three arms of first, second and third arms are sequentially attached from a base member, a robot hand is connected to a distal end portion of said third arm, said arms and robot hand are driven to rotate by driving force transmitted from a rotational driving source: wherein there are two states of folding directions of arm joints between a robot rotational center and a distal end portion of a robot hand with respect to a movement position of the robot hand, and wherein the robot comprises a control means which, when the robot hand moves in a forward direction, controls rotational motions of the arms so as to select one of said folding directions such that an angle between a robot hand direction and the third arm becomes 90xc2x0 or more.
In the above-mentioned composition, owing to the folding directions of the robot joints, the distal end portion of the second arms is always positioned behind the distal end portion of the third arm with respect to the forward direction of the robot hand. This makes it possible to decrease a robot arm movable area that makes no contribution toward conveying a workpiece.
Further, in the above-mentioned horizontal multi-joint industrial robot, the control means controls so as to change over the folding direction of the robot joints between both sides as a boundary line passing through the arm rotational center in parallel to the robot hand forward direction.
Furthermore, in the above-mentioned horizontal multi-joint industrial robot, said first and third arms are approximately equal in length, always parallel, and connected so as to rotate in a same direction, and wherein the first and second arms 2 and 3 are at a ratio of 1:2 in length.
According to another aspect of the present invention, there is provided a control method of a horizontal multi-joint industrial robot in which at least three arms of first, second and third arms are sequentially attached from a base member, a robot hand is connected to an distal end portion of said third arm, said arms and robot hand are driven to rotate by driving force transmitted from a rotational driving source: wherein there are two states of folding directions of arm joints between a robot rotational center and a distal end portion of a robot hand with respect to a movement position of the robot hand, and wherein, when the robot hand moves in a forward direction, rotational movement of the arms is controlled so as to select one of the folding directions such that an angle between a robot hand direction and the third arm becomes 90xc2x0 or more.
The above-mentioned control method controls so as to change over the folding direction of the robot joints between both sides as a boundary line passing through the arm rotational center in parallel to the robot hand forward direction.